A typical remote sensing system includes, among other things, optical fibers configured to convey the sensed data back to a central processor. Typical remote sensor locations suffer from both limited available electrical power and physical space. One conventional approach to providing the necessary electrical and electromagnetic interference (EMI) isolation between the remote sensors and the processor is to use an analog photonic link over optical fibers from the sensor or sensors to analog-to-digital converters (ADCs) located in proximity to the central (digital) processor. Another approach is to locate the ADCs in close proximity to the remote sensor(s) and send digitized data over the optical fibers. However, the power and space constraints at the remote location have proved difficult to overcome. Remotely locating ADCs over optical fiber at locations having both limited available electrical power and physical space has presented a particularly significant challenge.
Such remote sensing systems may be used for scientific data collection, geophysical measurements, hazardous environment testing, covert sensing, and similar missions. One typical application is collection of neutrino scintillation measurements from deep ice boreholes and oil prospecting.
Transmitting digitized data from remote ADCs over optical fiber has been achieved previously with implementations that require relatively high power and circuit complexity. Standard configurations use ADC devices having several output lines (e.g., N-bit parallel data lines or multiple serial lines with framing and clock signal lines) and require additional components to configure the ADC data before transmission. Previous techniques to properly format the ADC data for transmission over optical fiber data links have required high power consumption field programmable gate array (FPGA) or serializer devices. In addition, separate clock multiplication circuitry requiring significant power and space has been used to provide the necessary reference clock signals to the data serializer and multiplexer components. The power consumption of these previous configurations has often exceeded the available electrical power provided using conventional power-by-light (PBL) technologies and prevents an all optical fiber implementation of a remote ADC.
FIG. 1 depicts a high-level block diagram of a portion of a prior art remote sensor system 100 that employs an optical link. Here, remote front end module 110 consists of one or more sensors 120 and amplifiers 125 (one each shown for clarity). The amplified, analog data (typically wideband) is processed by photonic link 130 (such as by upconversion and modulation, for example) and transmitted over optical fiber 140 to base station receiver module 150. The analog data is detected and converted back to baseband by photodetector 160 and baseband components 170. Finally, the analog data is digitized in analog to digital converter (ADC) 180 and passed to processor 190 for processing. Various means for processing the wideband sensor data into forms suitable for analog transmission over optical fiber 140 are well known in the art.
Another prior art system for remote sensing (not shown) employs a conventional 14-bit parallel output ADC in the remote front end module instead of a photonic link. This system has a minimum of 15 data/signal output lines between the remote front end module and the base station receiver. It also requires additional components for correcting the serial format (such as an FPGA or serializer). Consequently, such a system suffers from high power consumption and complex packaging and integration issues.
Yet another prior art scheme uses a conventional 14-bit serial output ADC and a minimum of three data/signal output lines instead of an analog photonic link; the three data/signal outputs may be transmitted electrically or photonically to a base station. However, it still requires additional components for correcting the serial format (such as a serializer or other devices for framing and/or multiplexing). Such prior art systems also suffer from high power consumption and complex packaging and integration issues.
Thus, while prior art systems and techniques provide a desired level of electromagnetic interference (EMI) isolation, the prior art systems and techniques suffer from several disadvantages. In general, prior art systems and techniques are power-hungry and space-inefficient in the remote front end module due to the complexities of photonic link circuitry and numerous other circuit components.
What is needed is a complete EMI isolation solution that reduces or even minimizes the amount of space and power required in a remote front end while simplifying the overall architecture for remote sensing applications by locating the ADC near the sensor. Furthermore, it is desirable to eliminate analog photonic links and the related performance and maintenance problems caused by optical connectors carrying analog signals.